Born in 1817, Pierre Larousse undertook alone, from 1864 until his death in 1875, with immense energy and great freedom of spirit, his major work, the "Grand Dictionnaire Universel du XIXe Siècle", which he wanted to follow in the footsteps of Diderot and d'Alembert's Encyclopédie.

A committed democrat and republican, and an admirer ofAuguste Comte and of Pierre-Joseph Proudhon, Pierre Larousse made his Dictionary a tool for popularising republican ideas and spearheading the enlightened thinking of his century. He sympathised with the Paris Commune and welcomed Flourens after his release from Mazas, devoting a note to him in his dictionary. According to a statement by his great-niece, reported by his biographer André Rétif,

"Most of Pierre Larousse's workers were in the ranks of the Commune. Before taking up their posts, they would come in groups to bid farewell by throwing themselves into the boss's arms. Yes my children," said Pierre Larousse, crying with them, "I promise never to abandon your families, if they miss you, do your duty, my heart and my mind are with you.